1. Field of the Invention
The present invention relates to a photosensitive recording medium and a method of preparing a volume type phase hologram using the same.
2. Related Background Art
When a coherent light wave like a laser beam is projected onto an object, the amplitude and the phase of the light wave are modulated in accordance with the shape of the object. The modulated light reflected thereon or transmitted is received on a photo-sensitive recording medium and recorded, and a hologram thus formed is irradiated by light to reproduce an optical image.
With the development of the study on holography technique, requirements on the properties of recording mediums for holography have become more clear. Many materials are proposed for the hologram material, such as bleached silver halide, photoresists, thermoplastics, dichromated gelatin, inorganic glass materials, ferromagnetic materials, and the like, and the characteristics of the materials are being investigated comprehensively.
For example, bleached silver halide, and dichromated gelatin sensitized by Methylene Blue or the like are well known as a photosensitive hologram recording medium sensitive in a visible region.
U.S. Pat. No. 4,942,112 discloses a photopolymerizable composition composed of a polymer binder and an ethylenic unsaturated monomer having a carbazole ring or an aromatic ring for the photosensitive recording medium.
The properties required to the photosensitive recording medium for hologram are as follows:
(1) High recording sensitivity, in particular, high sensitivity to laser beam in visible region, PA1 (2) High resolution, PA1 (3) High diffraction efficiency of hologram, PA1 (4) Low noise in hologram, PA1 (5) Stability of hologram, and PA1 (6) Easiness of the operations of recording and reproduction.
These properties cannot readily be achieved. Only few of known recording mediums have some of the above properties at practically usable levels.
A bleached silver halide type recording medium and a dichromated gelatin type of recording medium are practically usable although not being completely satisfactory. However, the former type of medium has the disadvantages that they require bleaching treatment in addition to the usual treatments and the resulting hologram has low light-durability, and the latter type of medium has a serious defect of low water durability.
The recording mediums described in the aforementioned U.S. Pat. No. 4,942,112 are required to be improved to give larger refractive index modulation and to give a hologram of thinner film thickness.